1. Field of the Invention
The present invention relates to automatic and/or semi-automatic wire bonder and more particularly to a wire bonder having means for automatically positioning a semi-conductor relative to the bonding tool of the wire bonder at a second bond position.
2. Description of the Prior Art
Automatic wire bonders have been made which operate similar to numerical controlled machine tools. A semiconductor device to be wire bonded is placed in working position on the wire bonding machine and a plurality of wires, each having first and second bond positions, are attached to the semiconductor device and/or the supporting substrate. A program is generated by servo devices as the first semiconductor is manually wire bonded. The program of the first bonding pattern is recorded and may then be employed to duplicate the same routine of wire bonds on other semiconductors. The process of generating the program is referred to as the learning mode or the teaching mode, implying that subsequent devices are bonded with the program in a working mode. It is well known in the electronic data processing field that such programs may be stored in several types of memories which include solid state electronic memories of the type employed with programable electronic computing machines.
Automatic wire bonders employing solid state memories and solid state computing devices are expensive to build and are expensive to service or maintain. Automatic electronic programable wire bonders can be programmed to make both first and second wire bonds on a plurality of different devices. Since automatic electronic programable wire bonders produce a large number of bonds in a very short period of time, it is important to monitor the bonding operation to be sure that the operation is being performed correctly.
It has been the practice in the past to provide an operator on each automatic electronic wire bonder who observes the individual bonds to determine if malfunctions occur.
Semi-automatic wire bonders which perform a first bond and then automatically move the bonding tool rearward and upward to a position over a second bond position are known. U.S. Pat. No. 3,543,988 describes such a second bond positioning device, however, since the distances from the first bond positions to the second bond positions vary, the second bond position is not programmed for automatic bonding. Bonders of this type were not provided with means for individually programming each of the second bond positions but instead position the bonding tool at or near the second bond position enabling the operator to make a faster final position manually before activating the second bond.
It has been suggested that a wire bonder embodying cams similar to those described in U.S. Pat. No. 3,543,988 could be employed to position an X-Y table supporting a work holder so that a semiconductor device thereon could be moved from a first bond position automatically. In theory the suggestion is feasible, however, the need for precision machining required to produce such cams presents a first problem. In practice the manner in which individual active chips are connected to a substrate presents a more formidable problem. The active semiconductor device usually has bonding pads at the outer perimeter representative of the first bond positions. the active semiconductor device is die bonded or attached to a substrate having a plurality of bonding pads surrounding the active chip which are representative of the second bond position. It has not been commercially practical to place an active chip in the exact center of orientation of the substrate so that the distances between the first and second bonds remain constant, nor has it been commercially feasible to provide the exact orientation between the active chip and different substrates. Accordingly, a set of cams for positioning an X-Y table are not useful for automatic wire bonders. When wire bonders are provided with X-Y positioning cams they may be employed to locate the second bond position after making a first bond position in a manner similar to that described in U.S. Pat. No. 3,543,988. If the cams are made extremely accurate and the second bond position pads are made larger, the second bond may be programmed to be made automatically after the first wire bond position is made manually and the first bond made. Such devices do not provide self-teaching of a first or a second bond position.
In the prior art employing automatic wire bonders, self-teaching may be accomplished by actually making wire bonds at the first and/or the second bond positions. A preferred manner of self-teaching a bond position is to employ a very fine beam of light from an aiming device which is adjusted to provide a spot of light from the spotlight at the exact point where the bonding tool will attach the wire to the bonding pads. The bond positions can be entered into a program automatically for use in an automatic electronic wire bonder. An aiming device of the type used to locate bond positions without engaging the bonding tool is described in U.S. Pat. No. 3,661,316.
Heretofore, automatic electronic wire bonders have been provided with means for self-teaching the first and the second bond position. Such self-teaching means comprise expensive servos which generate program data capable of being repeated.
Heretofore, mechanical wire bonders having cams for establishing an exact or approximate second bond position were not provided with any device for self-teaching the second bond positions.
It would be extremely useful to provide an inexpensive, reliable, fast acting electro mechanical wire bonder which would automatically perform second wire bonds after a first wire bond has been made manually and which could be self-taught or programmed to achieve the second bond in the manner now achieved by expensive automatic electronic wire bonders.